1. Field of the Invention
The present invention relates to a relief valve for an oil pump that is particularly suitable for an internal combustion engine for power generation of an electric automobile, includes a relief valve and a temperature sensitive valve, enables execution of a relief (oil discharge) operation in a pressure rise irrespective of the level of the temperature of oil, and can be simplified in a configuration thereof.
2. Description of the Related Art
In recent years, electric automobiles are increasing. The electric automobiles have various types of power generation systems. Among the power generation systems, a range extender is suitable for the electric automobiles. In the range extender, an internal combustion engine and a generator are mounted on an automobile. The engine performs charging of the generator. The generator drives a drive motor to enable the automobile to travel.
As an oil pump for supplying oil to an engine to lubricate the engine, there are various oil pumps including a relief valve that performs relief when a discharge pressure exceeds a predetermined value. Further, there are a large number of relieve devices for oil pumps of a type for determining whether relief is executed according to a pressure change and a temperature change of oil.
Japanese Patent Application Laid-open No. 2006-214286 discloses a representative example of the relief valves of this type. An embodiment (a third embodiment) including a second control valve 7 among a plurality of embodiments disclosed in Japanese Patent Application Laid-open No. 2006-214286 is summarized. Note that signs used in Japanese Patent Application Laid-open No. 2006-214286 are used as they are. In an oil pump X, hydraulic oil from a pump main body 1 is discharged only from a single discharge port 31. A first control valve 4 functions only as a relief valve when a discharge pressure of the hydraulic oil in a discharge oil passage 5 is high. The second control valve 7 is a valve that operates according to the temperature of the hydraulic oil to control the first control valve 4 and, specifically, controls the hydraulic pressure of the hydraulic oil flowing into a second valve chamber 44 of the first control valve 4.
In the oil pump X, the second control valve 7 is maintained in a normal state when the temperature of the hydraulic oil is in a normal temperature range lower than about 110° C. The first control valve 4 operates according to a discharge pressure of the hydraulic oil discharged to the discharge oil passage 5. When the discharge pressure of the hydraulic oil rises, the first control valve 4 causes a first valve chamber 43 and a return port 41d to communicate with each other and supplies a part of the hydraulic oil in the discharge oil passage 5 to a return oil passage 6 to thereby perform relief of the discharge pressure.
When the temperature of the hydraulic oil is high, the first control valve 4 performs control without operating as the relief valve. Therefore, it is possible to design the oil pump X to have an optimum characteristic of the discharge pressure in the normal temperature range lower than about 110° C., which is a temperature range of the hydraulic oil under a normal condition of use, while securing a necessary discharge pressure of the hydraulic oil when oil is at a high temperature.
A relief valve device that performs a complicated operation disclosed in Japanese Patent Application Laid-open No. 2006-214286 is suitable for an oil pump for an engine in an automobile including only an internal combustion engine. However, in the electric automobile explained above, the engine plays the roles for power generation and charging of the generator. Therefore, the speed of the engine is substantially fixed. An intermediate engine speed region only has to be maintained.
As explained above, in the electric automobile, compared with the engine used for only power generation, the relief device disclosed in Japanese Patent Application Laid-open No. 2006-214286 has a drawback in that a hydraulic pressure reduction effect is small and only costs increase. In particular, since relief is not performed when the temperature of the hydraulic oil is high, it is likely that energy is wastefully consumed.